Senate Republicans aren’t just widening their path to the majority with each new seat added to the competitive map, they’re also increasing the odds Democrats will have to spend money in states beyond the top battlegrounds.

Faced with such a lopsided map this cycle, Senate Democrats were undoubtedly budgeting to spend in at least 10 states. The party is defending nearly two-thirds of the three dozen seats up in November, and a third of their seats are in states President Barack Obama lost in 2012.

But as Republicans continue to fill their candidate roster in potentially competitive races — most recently adding Rep. Cory Gardner in Colorado — it means more money Democrats may have to spend on seats not among their most vulnerable.

“When you expand the playing field, it really does change the dynamics of what you’re planning on doing,” said Dan Allen, a Republican consultant and former operative at the National Republican Senatorial Committee. “It’s one more you’re adding to the list that you’re going to have to be fighting for and also spending and dedicating resources in. That’s where the math becomes problematic.”

Gardner’s recent decision to challenge Democratic Sen. Mark Udall likely altered the Democratic Party’s estimates of how much money it would be forced to spend there this fall, even though the party remains confident about Udall’s chances to prevail.

To be sure, in a swing state such as Colorado in a midterm cycle, the Democratic Senatorial Campaign Committee and Democrat-aligned outside groups might have felt compelled to expend resources against Ken Buck, who was waging his second Senate campaign until Gardner entered the race. Buck’s flaws as a candidate were exposed during his unsuccessful 2010 Senate campaign, when the DSCC spent about $8 million defending Michael Bennet in a cycle that cost Democrats six seats.

As other races emerge as potential trouble spots for the DSCC, the party’s money may end up spread more widely than it hoped in a cycle where a similar six-seat loss would this time cost Democrats the majority. The DSCC maintains that the party is prepared.

“Democrats will have the resources necessary to successfully wage top-tier competitive campaigns in all of our races that contrast a Democrat who is fighting for their state with a reckless and irresponsible Republican who is pushing a special interest agenda that’s good for the Koch Brothers and bad for everyone else,” DSCC spokesman Justin Barasky said.

With primary season kicking off just last week, the map remains fluid. The competitiveness of a state like Iowa, where Democrats are defending an open seat, could diminish depending on who emerges from the complicated GOP nomination process this summer. Republicans are also hoping early polls in Michigan prove prophetic for the fall and that former Sen. Scott P. Brown, R-Mass., finally jumps into the New Hampshire Senate race — though both are far from a sure thing.

Conversely, Democrats recruited former Rep. Travis Childers in Mississippi in preparation for a possible tea-party-primary upset of longtime Republican Sen. Thad Cochran. That could force the National Republican Senatorial Committee to shell out money to defend the seat. And the NRSC may have to do the same to boost Senate Minority Leader Mitch McConnell in Kentucky, and to keep Democrats from flipping the GOP-held open seat in Georgia. At this point, the Rothenberg Political Report/Roll Call finds the Republicans remain favored in all three contests.

The sheer number of offensive opportunities for Republicans gives the party a shot at winning the majority for the first time since Democrats took control in the 2006 midterms. The president’s national approval rating — hovering below 50 percent — isn’t helping his party, especially in a midterm cycle when the only avenue to vote against him is via his party in congressional races.

Still, Democrats have a few financial factors working in their favor. The DSCC has outraised the NRSC by $18 million so far this cycle, Democratic incumbents and candidates are all raising strong sums of money and nearly all of the top-tier Senate races this cycle are in states with relatively inexpensive media markets.

That includes the open seat in West Virginia, and the seats of some of its most endangered incumbents: Sens. Mark Begich of Alaska, Mark Pryor of Arkansas, Mary L. Landrieu of Louisiana and appointed Sen. John Walsh of Montana. Democrats have not signaled any intent to spend in the party’s most vulnerable open-seat race, in South Dakota.

But late in every cycle, party committees must grapple with where to invest limited resources. In 2010, the DSCC opted not to spend to help Arkansas Sen. Blanche Lincoln or the Democrat who unsuccessfully bid for the open New Hampshire Senate seat. The NRSC faced the same issues in 2006, as Republicans lost the majority thanks to unforeseen competitive races in Virginia and Montana.

At the time, GOP operatives openly blamed George Allen for losing to Democrat Jim Webb in a Virginia race that should not have been expensive nor competitive.

With GOP-aligned outside groups such as Americans for Prosperity already pouring money into Senate races, particularly against Sen. Kay Hagan, D-N.C., it complicates the situation. But Democratic strategists maintain that the GOP’s ability to field legitimate candidates in potentially competitive races this cycle is not sending the party scrambling.

“We have long said, and long planned, to be involved in every competitive race, so we will marshal the necessary resources to compete,” said Ty Matsdorf of the Democrat-aligned Senate Majority PAC.